USB_DM：data minus 负， D-（白色）
USB_DP：data plus 正，D+（绿色）
VCC 是电源5V（红色）
GND 是地（黑色）
USB插头线一般的排列方式是GND、D+、D-、VCC
附：各种USB接口线序（此图来自网络）
问题：
~ # usb 1-1: new high-speed USB device number 2 using ehci-platform
usb 1-1: device descriptor read/64, error -71
usb 1-1: device descriptor read/64, error -71
usb 1-1: new high-speed USB device number 3 using ehci-platform
usb 1-1: device descriptor read/64, error -71
usb 1-1: device descriptor read/64, error -71
usb 1-1: new high-speed USB device number 4 using ehci-platform
usb 1-1: device not accepting address 4, error -71
usb 1-1: new high-speed USB device number 5 using ehci-platform
usb 1-1: device not accepting address 5, error -71
usb usb1-port1: unable to enumerate USB device
原因：
源代码中的-71(/include/asm-generic/erro.h)代表的是协议的错误，协议的错误可以理解为信号的异常，时序的偏差。
解决方法：
检查线是否接触良好，以及双绞线的密度。
正确结果:
~ # usb 1-1: new high-speed USB device number 2 using ehci-platform
option 1-1:1.0: GSM modem (1-port) converter detected
usb 1-1: GSM modem (1-port) converter now attached to ttyUSB0
option 1-1:1.1: GSM modem (1-port) converter detected
usb 1-1: GSM modem (1-port) converter now attached to ttyUSB1
option 1-1:1.2: GSM modem (1-port) converter detected
usb 1-1: GSM modem (1-port) converter now attached to ttyUSB2
option 1-1:1.3: GSM modem (1-port) converter detected
usb 1-1: GSM modem (1-port) converter now attached to ttyUSB3
